Transparent conductors, such as Indium Tin Oxide (ITO), combine the electrical conductivity of metal with the optical transparency of glass and are useful as components in electronic devices, such as in display devices. Flexibility is likely to become a broader challenge for ITO, which does not seem well suited to the next generation of display, lighting, or photovoltaic devices. These concerns have motivated a search for replacements using conventional materials and nanomaterials. There is variety of technical approaches for developing ITO substitutes and there are four areas in which these various alternatives compete: price, electrical conductivity, optical transparency, and physical resiliency.
Electrically conductive polymers, such as polythiophene polymers, particularly a polymer blend of poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate) (“PEDOT-PSS”) have been investigated as possible alternatives to ITO. The electrical conductivity of electrically conductive polymers is typically lower than that of ITO, but can be enhanced through the use of conductive fillers, such as carbon nanotubes, and dopants. However, the performance of such films still falls short of that of ITO and trade-offs exist between optimizing the electrical conductivity and optimizing the optical transparency of electrically conductive polymers films.
There has been some interest in modifying the properties of electrically conductive polymer films using ionic liquids. U.S. Pat. No. 842,197, issued Nov. 30, 2010, broadly discloses mixtures of electrically conductive polymers and ionic liquids, including specifically, mixtures of PEDOT-PSS and 1-butyl-3-methyl-imidazolium tetrafluoroborate. U.S. Pat. No. 7,842,197, issued Nov. 30, 2010, discloses a method for producing a conductive material by contacting an electrically conductive polymer with certain ionic liquids U.S. Patent Application Publication 2008/0139710 A1, published Jun. 12, 2008, discloses conductive gels comprising certain conductive polymers dispersed or dissolved in certain ionic liquids, in combination with certain gelling agents.
There is an ongoing unresolved interest in increasing the electrical conductivity and optical transparency of electrically conductive polymer films, more specifically of PEDOT-PSS films.